Scroll down to to the last link to find a video someone took from their (albeit very dirty) window of Saoirse Ronan and Timothee Chalamet filming a scene.

EDIT 2:43 CST, October 7th: Many T-Mo fans believe that this is not Timothee, but rather Louis Garrel. However, the height and the hair match Timothee's and we know that Timothee went out to dinner in Boston with Saoirse and James Norton in Concord, Mass on the 28th of September. Also, the videographer doesn't say when he actually took the video, so it very well could be Louis.

What do you think?

Also, as a bonus, here is a new photo of Timothee and Saoirse at the aforementioned restaurant!